Frequency conversion system with improved spurious response and frequency agility

Abstract

A frequency conversion system with improved performance. In one embodiment an image reject mixer is used to perform frequency conversion providing an initial degree of suppression of the image and local oscillator leakage signals, and a signal to noise enhancer (SNE) is used to further suppress the image and local oscillator signals, the signal to noise enhancer being a nonlinear passive device that attenuates low-power signals while transmitting high power signals with little loss. The signal to noise enhancer may be fabricated as a thin film of yttrium iron garnet (YIG) epitaxially grown on a gadolinium gallium garnet (GGG) substrate, the GGG substrate secured to a microwave transmission line from the input to the output of the signal to noise enhancer, such that the thin film of yttrium iron garnet is close to the transmission line.

What is claimed is: 
     
       1. A system for frequency conversion, the system comprising:
 an image reject mixer, configured:
 to receive a local oscillator input signal and a modulation signal, and 
 to produce a modulated output signal, comprising:
 a first modulation sideband signal, 
 a local oscillator output signal, and 
 a second modulation sideband signal, 
 
 the power in the local oscillator output signal being at least 5 decibels (dB) less than the power in the first modulation sideband signal, and 
 the power in the second modulation sideband signal being at least 5 dB less than the power in the first modulation sideband signal; and 
 
 a signal-to-noise enhancer (SNE) having:
 an input connected to receive the modulated output signal from the image reject mixer; and 
 an output, 
 the SNE comprising:
 a microwave transmission line connected between the input and the output of the SNE; 
 a magnetic component capable of supporting magnetostatic waves, the magnetic component secured in proximity to the microwave transmission line; 
 one or more magnets secured in proximity to the magnetic component; 
 
 the SNE having the characteristic of allowing a signal to propagate from the input of the SNE to the output of the SNE:
 with a first attenuation when the power of the signal at the input of the SNE is less than a first threshold, and 
 with a second attenuation when the power of the signal at the input of the SNE is greater than a second threshold, 
 
 the first attenuation exceeding the second attenuation by at least 5 dB. 
 
 
     
     
       2. The system of  claim 1 , wherein the magnetic component comprises a thin film of yttrium iron garnet (YIG) on a gadolinium gallium garnet (GGG) substrate. 
     
     
       3. The system of  claim 2 , wherein the thin film of YIG is a single crystal of YIG, the GGG substrate is a single crystal of GGG, and the thin film of YIG is lattice-matched to the GGG substrate. 
     
     
       4. The system of  claim 1 , wherein a portion of the transmission line in proximity with the magnetic component follows a substantially straight path. 
     
     
       5. The system of  claim 4 , wherein the one or more magnets comprise two magnets, positioned and oriented with respect to the portion of the microwave transmission line so as to produce, in the magnetic component, a biasing magnetic field substantially parallel to the portion of the microwave transmission line. 
     
     
       6. The system of  claim 1 , wherein the image reject mixer comprises:
 a first intermediate frequency (IF) mixer comprising a first input, a second input, and an output; 
 a second IF mixer comprising a first input, a second input, and an output; 
 a first filter comprising an input and an output; and 
 a second filter comprising an input and an output, 
 the first input of the first IF mixer being connected to the input of the image reject mixer, 
 the output of the first IF mixer being connected to the input of the first filter 
 the first input of the second IF mixer being connected to the input of the image reject mixer, 
 the output of the second IF mixer being connected to the input of the second filter, and 
 the output of the first filter and the output of the second filter being connected to the output of the image reject mixer. 
 
     
     
       7. The system of  claim 6 , wherein a combiner is connected between the output of the first filter and the output of the image reject mixer, and the combiner is connected between the output of the second filter and output of the image reject mixer. 
     
     
       8. The system of  claim 6 , wherein the first filter is a polyphase filter and the second filter is a polyphase filter. 
     
     
       9. The system of  claim 6 , further comprising:
 a first variable gain amplifier connected between the output of the first IF mixer and the input of the first filter, and 
 a second variable gain amplifier connected between the output of the second IF mixer and the input of the second filter. 
 
     
     
       10. The system of  claim 9 , further comprising:
 a third variable gain amplifier connected between the output of the first variable gain amplifier and the input of the first filter, and 
 a fourth variable gain amplifier connected between the output of the second variable gain amplifier and the input of the second filter. 
 
     
     
       11. The system of  claim 10 , wherein the gain of the third variable gain amplifier is adjustable in increments of 1 decibel (dB) or less. 
     
     
       12. The system of  claim 6 , further comprising:
 a first phase shifter comprising one or more inputs and an output; and 
 a second phase shifter comprising one or more inputs and an output; 
 the output of the first phase shifter being connected to the second input of the first mixer, and 
 the output of the second phase shifter being connected to the second input of the second mixer. 
 
     
     
       13. The system of  claim 12 , wherein each of the first phase shifter and the second phase shifter comprises:
 an in-phase input; 
 a quadrature input; 
 a first variable gain amplifier comprising an input and an output; 
 a second variable gain amplifier comprising an input and an output; and 
 a combiner comprising a first input, a second input and an output, 
 the in-phase input being connected to the input of the first variable gain amplifier, 
 the quadrature input being connected to the input of the second variable gain amplifier, 
 the output of the first variable gain amplifier being connected to the first input of the combiner, and 
 the output of the second variable gain amplifier being connected to the second input of the combiner. 
 
     
     
       14. The system of  claim 13 , wherein each of the first and second variable gain amplifiers is a digitally controlled variable gain amplifier. 
     
     
       15. The system of  claim 13 , wherein each of the first phase shifter and the second phase shifter further comprises a limiter connected to the output of the combiner and configured to regulate the amplitude of the output of the combiner to a constant amplitude. 
     
     
       16. The system of  claim 1 , further comprising an amplifier connected between the output of the image reject mixer and the input of the SNE. 
     
     
       17. The system of  claim 16 , wherein the amplifier has a gain selected to provide an input power level greater than the second threshold at the input of the SNE.